Beta cell replacement strategies for the future management of insulin-dependent diabetes will require amplification of pancreatic islet tissue in Vitro for transplantation or induction of new islets by stimulating islet growth within the diabetic patient. Accordingly, a fundamental issue is to identify mechanisms that regulate the development and death of B cells. Towards this end, studies of animal models with experimentally augmented islet mass have generally entailed some form ol pancreatic trauma whereby the identification of the mechanisms involved are confounded by responses to injury. The relative importance of new islet formation from ducts (neogenesis) vs. B cell hyperplasia in existing islets during B\ cell mass expansion in the adult pancreas, as well as the growth factors and signaling pathways that control these two processes, are unknown. The primary goal of this proposal is to investigate islet neogenesis and B hyperplasia in rats undergoing compensatory B cell growth from a glucose infusion (i.e., no direct pancreatic manipulation). We will specifically (1) determine the extent of islet neogenesis vs. B cell growth occurring in glucose-infused rats under hyperglycemic and normoglycemic conditions, (2) investigate the developmental relationships of the cells involved in islet neogenesis based on the expression of key islet transcription factors and B cell functional markers, and (3) analyze the potential role of the insulin signaling cascade during glucose-induced islet neogenesis by examining the cell-specific expression and activation of insulin receptor substrate-2 and protein kinase B/Akt. These studies will establish the foundation for future endeavors to identify and exploit signaling pathways, and the stimulating ligands involved, in order to manipulate islet neogenesis.